问题补充：
30. —Why! I get you on the phone.
— We basketball on the playground when you phoned.
A. didn’t; must have been playing
B. didn’t; must be playing
C. couldn’t; must have played
D. couldn’t; must be playing
答案：
(答案→)A. didn’t; must have been playing
B. didn’t; must be playing
C. couldn’t; must have played
D. couldn’t; must be playing
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